Refrigeration system



Nov. 22, 1955 H. SLOAN 2,724,240

REFRIGERATION SYSTEM Filed Oct. 25, 1952 INVENTOR. T Wd/Zazz/n/ H BY g & W A rro FIVE/6'.

United States Patent Ofilice 2,724,240 Patented Nov. 22, 1955 REFRIGERATION SYSTEM Harry Sloan, Waukesha, Wis., assignor to The Vilter Manufacturing Co., Milwaukee, Wis., a corporation of Wisconsin Application October 25, 1952, Serial No. 316,843

12 Claims. (Cl. 62-3) This invention relates generally to improvements in the art of refrigeration, and relates more specifically to improvements in the construction and operation of instrumentalities for automatically returning liquid refrigerant delivered from the low or evaporator side to the high pressure side of a refrigeration system in orderto prevent liquid refrigerant from entering and damaging the con1 pressor, and to also make the liquid available for per forming useful work.

The primary object of the present invention is to provide a simple and reliable system for returning liquid refrigerant directly from the low or evaporator discharge side of a refrigeration installation, to the high pressure refrigerant supply side of the system.

When operating refrigeration installations of large capacity having numerous cooling coils or evaporators, it is customary to provide a separator communicating with the suction or outlet side of the evaporators for removing the liquid refrigerant from the vapor, and for collecting the liquid in an accumulator from which it may be returned to the receiver or high pressure line without entering the compressor which circulates the refrigerant through the system. Several different modes of returning the liquid refrigerant deposited within the accumulator to the high pressure side of the compressor in such large installations, have heretofore been proposed, but all of the prior systems are either too complicated and unreliable or they require too much attention, in order to make them entirely satisfactory.

It is therefore an important object of my present invention to provide improved means for effecting return of liquid refrigerant derived from the outlet or suction side of the evaporators of a refrigeration system, directly to the high pressure liquid supply side of the evaporators, automatically and in a most reliable and effective manner.

Another importantobject of the invention is to provide an improved liquid refrigerant return and compressor by passing system for large capacity refrigeration plants, which functions effectively with the aid of a low differential pressure pump cooperating with a simple automatic control system operable by variations in the quantity of liquid refrigerant in the low pressure side of the system.

A further important object of this invention is to provide an improved refrigeration system provided with a refrigerant circulating compressor having a suction li e for receiving evaporated refrigerant through a separator from an evaporator and also having a discharge line for delivering liquid refrigerant to a receiver communicable with the evaporator through a high pressure refrigerant line past an expansion valve or the like, and having automatic means for returning liquid refrigerant derived from the separator directly to the receiver or high pressure side.

Still another importantobject of the present invention is to provide various improvements in the mode of bypassing the compressor and of returning liquid refrigerant from the suction to the high pressure supply line of the evaporators of commercial refrigerating installations whereby the operation of such systems is vastly facilitated and improved economy of operation is attained.

These and other objects and advantages of the invention will be apparent from the following description from which it will be noted that the gist of the improvement is the use of a low differential pressure pump which cooperates with valves for periodically equalizing the pressures in the accumulator and receiver of the refrigeration system, so as to return excess liquid refrigerant derived from the evaporators from the accumulator to the receiver in a manner whereby the only work performed by the pump is to overcome the static head and friction through connections, and the power required to drive the pump is only a small fraction of that required by a pump having unbalanced head and suction pressure.

A clear conception of the features constituting my present improvement, and of the mode of constructing and operating a typical commercial refrigeration system embodying the invention, may be had by referring to the drawing accompanying and forming a part of this specification wherein like reference characters designate the same or similar parts in the various views.

Fig. l is a diagram of an improved refrigeration installation embodying my automatic liquid refrigerant return system; and

Fig. 2 is a typical wiring diagram for actuating the low differential pressure pump and its control devices.

Referring to the drawing, the typical refrigeration system illustrated diagrammatically therein, comprises in general, a main compressor 4 having a suction line 5 for receiving evaporated refrigerant or vapor through one or more outlet lines 6 and a separator 7 from one or more cooling coils or evaporators 8, and also having a delivery pipe 9 for discharging high pressure refrigerant by way of a condenser 10 and a receiver 11 to the evaporators 8 through high pressure lines 12 and past expansion valves 13; an accumulator 14 for collecting liquid refrigerant removed by the separator 7; a pipe or conduit 15 connecting the accumulator 14 with the receiver 11 and having therein a low differential pressure pump 16 driven by an electric motor 17, and also having a non-return check valve 18 therein between the pump 16 and the receiver 11; upper and lower float actuated switches 19, 20 respectively, operable by variations of the level of liquid refrigerant within the accumulator 14 to control the operation of the pump motor 17; and a plurality of solenoid valves 21, 22, 23 for effecting equalization of the pressures in the accumulator 14 and separator 7 whenever the operation of the pump 16 is interrupted, and for establishing receiver pressure within the accumulator 14 when the pump 16 is operating.

The compressor 4 is adapted to be driven by an electric motor 25 or the like, through a belt drive 26, and this compressor 4 as well as the separator 7, evaporators 8, condenser 10, receiver 11, and expansion valves 13, may all be of conventional and well known design, construction and operation. The lower portion of the accumulator 14 is connected to the inlet side of the pump 16 by a conduit 27, and the upper portion of this accumulator is connected to the lower liquid refrigerant discharge portion of the separator 7 by a pipe 28 in which the magnetically actuated valve 23 is located and this upper accumulator portion preferably exposes limited liquid surface area to the entering high pressure gases in order to hasten the equalization of pressures and to retard condensation, see Fig. l. The upper vapor chamber of the separator 7 which is in open communication with the suction lines 5, 6, is adapted to be connected with the upper portion of the accumulator 14 through the magnetically actuated valve 21 and a pipe 29 Whenever the valve 23 is open; and the receiver 11 is adapted to be connected to the upper portion of the accumulator 14 through the pipe 29, magnetically actuated valve 22 and another pipe 30, whenever the valves 21, 23 are closed. ,Thc magnetically actuated solenoid valves 21, 22, 23 and the float actuated switches 19, 2t) may be of any suitable type well known to the refrigeration industry, and the low differential pressure pump 16 is of any type suitable for the existing pressure conditions and may be operable by the motor 17 which is adapted to be connected to the main electric current supply line 32 through an automatic starter 33, shown in Fig. 2. The starter 33 which is periodically operable to start and stop the motor 17 and pump 16, is actuated through a magnetic relay 34 by the float controlled switches 19 20 associated with the accumulator 14, and also functions to automatically control the operation of the magnetic valves 21, 22, 23, but this starter and the relay may also be of any suitable type the operation of which is well known, and which are readily available on the market.

When the improved refrigerant return system has been properly constructed and installed, its operation is as follows. At the beginning of each cycle of operation, the pump 16 is idle with both switches 19, 20 open and the solenoid valve 22 closed, while the valves 21, 23 will be opened so as to equalize the pressures in the separator '7 and accumulator 14 through the pipes 28, 29 and to thereby permit liquid refrigerant which is being separated from the refrigerant withdrawn from the evaporators 8 through the suction line 6 by the main compressor 4, to flow by gravity into the accumulator 14. When the level of the liquid refrigerant thus deposited in the accumulator 14 reaches the level of the float actuated switch 20, this switch closes but does not cause electric current to flow because the circuit is still open at the float actuatcd switch 19. As the liquid refrigerant in the accumulator 14 continues to rise the float actuated switch 19 eventually closes, completing the electric circuit so as to energize the operating coil of the magnetic relay 34. Electric current will then flow from the terminal L" of the starter 33 to the junction Y and into the operating coil of the relay 34 at L, out of the coil at M into the float actuated switch 19 at K, out of this switch at I, through the junction W into the float actuated switch 20 through the terminal G, out of this switch at the terminal H, through the junctions U and V, and back to the starter terminal L. When the magnetic relay 34 is thus energiied, the contact is closed between the terminals F and C, and also between the terminals E and B, but at the same moment contact between the terminals D and A is interrupted. As the circuit between the terminals F and C on the relay 34 is completed, the uper float actuated switch 19 is rendered inoperative because the electric current for actuating this relay 34 is then supplied through the relay coil from the terminal L" on the starter 33 through the junction T to the terminal C, across to the terminal F and on to the junction W, and then to the terminal G on the float actuated switch 20, whereupon the relay 34 is held closed by its own contact across the terminals F and C.

When the magnetic relay 34 is energized, electric current is supplied to the starter coil from the terminal L" then through the terminal to the junction Z and from there to the terminal B on the relay. This contact being closed, the current flows through to the terminal E and junction U, then on to the terminal L on the starter 33, thereby starting the motor 17 which drives the pump 16. The valves 21 and 23 close when the time relay 34 is energized because the circuit through the contacts at the terminals D and A of the relay 34, is opened. The electrtc circuit to the valve 22 is closed within the relay 34 through the contacts connected to the terminals E and B, which opens this valve simultaneously with the energization of the starter 33.

The switch 19 opens as soon as the liquid level drops below its float inlet but the switch 20 does not open 4 until the accumulator 14 is practically empty, and the opening of the solenoid valve 22 immediately equalizes the pressures in the receiver 11 and accumulator 14 through the pipes 29, 30 while refrigerant vapors may continue to flow through the separator 7 and suction lines 5, 6. The low pressure pump 16 will then remove liquid refrigerant from the lower portion of the accumulator 14 through the conduit 27 and will deliver the liquid through the conduit 15 and past the check valve 18 to the receiver 11, while being subjected only to the static head of liquid within the conduit 15. When liquid refrigerant has been thus returned from the accumulator 14 to thereceiver 11 sufficiently to cause the lower float actuated switch 20 to open, then the relay 34 will be de-energized because the circuit across the terminals H and G of the float actuated switch 20 will be interrupted. When the magnetic relay 34 is de-energized, the circuit across the terminals E and B is interrupted causing the starter 33 to open and thereby stopping the motor 17 and the pump 16, and the circuit for opening the valve 22 through the same terminals is also interrupted thereby causing this valve to close. At the same time that the relay 34 is de-energized, an electric circuit is completed across the terminals D and A of this relay thereby causing the valves 21 and 23 to open, thus re-establishing the conditions existing at the beginning of the cycle of operation. I

This cycle of operations will be automatically repeated whenever the liquid level within the accumulator 14 actuates the float controlled switches 19, 20, without any attention on the part of the operators or attendants, and without the use of auxiliary traps, drums, or unreliable and exceedingly complicated valve mechanisms and other accessories. Since the liquid return pump 16 operates only against the static head of liquid refrigerant within the conduit 15, a very inexpensive pump operable with minimum power consumption may be utilized, and because this pump operates under only slight differential pressure it also prevents annoyance in operation due to the presence of flash gas within the pump such as frequently occurs in refrigerant circulating pumps that handle liquid refrigerant at its boiling point and operate under high differential pressures.

From the foregoing detailed description it will be apparent that the present invention in fact provides an improved refrigeration system of the direct expansion type wherein the liquid refrigerant delivered from the evaporators is automatically and eflectively returned to the high pressure side of the system with the aid of simple and reliable equipment. The operation of'the pump 16 so as to cause it to operate under minimum pressurediffei'ential, is effectively controlled by the simple float switches 19, 20, and by the relatively simplesolenoid valves 21, 22, 23 and the check valve 18 which func-' tions to alternately equalize the pressures between the separator 7 and accumulator 14 when liquid refrigerant is being deposited by gravity within the latter, and between the accumulator 14 and receiver 11 when the accumulate'd liquid refrigerant is being transferred from the former to the latter. The more nearly that equalization of pressures on opposite sides of the pump 16 is effected, the less power is required to drive this pump; and when the improved system is operating, the noncondensible gases collect in the top of the receiver ll and are removed to the accumulator 14 from which they escape to the separator 7 and from there to the main compressor 4, thus preventing these gases from trapping in the receiver and cooling coils. The valves 21, 22, 23 also function to prevent direct communication between the separator 7 and receiver 11, and to permit free flow of vapor to the compressor 4 while liquid is being by-pass'ed to the receiver.

The important features of the present invention are that it eliminates the presence of flash gas in the low pressure side of the system, and it enables the use of a l miner return pump which alwaysif requires the, same horsepower regardless of H variations r in the pressure conditions existing in the system Inprior systems, if the system is operating at say minus40 degrees suction and the condenser pressurelis 200 pounds, it, is necessary to furnish two pumps operatingjin series in order to produce satisfactory results. With my improved system only a single pump operable under considerably less differentialpressure and with lower horsepowerconsumption, maybeutilized. The equalization of the accumulator andpunip discharge pressures in the improved system avoids necessity of having the pump handle liquid refrigerant atits boiling point and thus eliminates formationfof flash gas which has heretofore caused severe knocking and damage to pumpjs due to sudden condensation of such gases.

It should be understood that it is not desired to limit this invention to the exact details of construction and operation of the refrigerant return system, herein specifically shown and described, for various modifications within the scopeof theappended claims may occur to persons skilledin the art. t

Iclaim: b

1. In a refrigerating system provided with a compressor having a suction line forreceiving evaporated refrigerant through a separator from an evaporator and also having a discharge line for delivering liquid refrigerant to a receiver communicable with the evaporator through a high pressure refrigerant line past an expansion valve, an accumulator for collecting liquid, refrigerant removed from the suction line, conduit means connecting said accumulator with the receiver and having therein a low differential pressure pump and a non-return check valve between thelpump and receiver, means for effecting operation of said pump whenever the level of liquid refrigerant in said accumulator reaches a predetermined high value and for interrupting said operation when said liquid level drops to a predetermined extent, valve means for effecting equalization of the pressures in said accumulator and separator whenever said pump operat1on is interrupted, and other means cooperable with said valve means to establish receiver pressure within said accumulator whenever said pump is operating.

2. In a refrigerating system provided with a compressor having a suction line for receiving refrigerant through a separator from an evaporator and also having a discharge line for delivering liquid refrigerant to a receiver communicable with the evaporator through a high pressure refrigerant line past an expansion valve, an accumulator for collecting liquid refrigerant removed from the suction line, conduit means connecting said accumulator with the receiver and having therein a low differential pressure pump and a non-return check valve between the pump and receiver, means for equalizing the pressures in said accumulator and separator and for stopping said pump whenever liquid refrigerant is flowing from the separator to the accumulator, and means for equalizing the pressures in said accumulator and receiver and for operating said pump whenever the level of liquid refrigerant within the accumulator has reached a predetermined height.

3. In a refrigerating system provided with a compressor having a suction line for receiving refrigerant through a separator from an evaporator and also having a discharge line for delivering liquid refrigerant to a receiver communicable with the evaporator through a high pressure refrigerant line past an expansion valve, an accumulator for collecting liquid refrigerant removed from the suction line, conduit means connecting said accumulator with the receiver and having therein a low differential pressure pump and a non-return check valve between the pump and receiver, valve means for effecting equalization of the pressures in said accumulator and separator while permitting drainage of liquid refrigerant from the separator into the accumulator while said pump is stopped, and other valve means for effecting equalization of the pressures in said accumulator and receiver" while permitting operation of said pump to transfer liquid refrigerant from the accumulator to the receiver,

4. In a refrigerating system provided with a compres sor having a suction line for receiving refrigerant through a separator from an evaporator and also having a discharge line for delivering liquid refrigerant to a receiver communicable with the evaporator through a high pressure refrigerant line past an expansion valve, an accumulator for collecting liquid refrigerant removed by the separator, conduit means connecting said accumulator with the receiver and having therein a motor driven low differential pressure pump and a non-return check valve between the pump and receiver, a float actuated switch for effecting operation of said pump whenever the level of liquid refrigerant in said accumulator reaches a predetermined high value, and another float actuated switch for interrupting said operation when said liquid level drops to a predetermined extent, valve means for effecting equalization of the pressures in said accumulator and separator Whenever said pump operation is interrupted, and other valve means cooperable with said first mentioned valve means to establish receiver pressure within said accumulator Whenever said pump is operating.

5. In a refrigerating system provided with a compressor having a suction line for receiving refrigerant from an evaporator and also having a discharge line for delivering liquid refrigerant to a receiver communicable with the evaporator through a high pressure refrigerant line, an accumulator for collecting liquid refrigerant removed from the suction line, conduit means connecting said,

accumulator with the receiver and having therein a low differential pressure pump, means for effecting operation of said pump whenever the level of liquid refrigerant in said accumulator reaches a predetermined high value and for interrupting said operation when said liquid level drops a predetermined amount, means for effecting equalization of the pressures in said accumulator and the suction line Whenever said pump is inactive, and other means for establishing receiver pressure within said accumulator whenever said pump is active.

6. In a refrigerating system provided with a compressor having a suction line for receiving refrigerant from an evaporator and also having a discharge line for delivering liquid refrigerant to a receiver communicable with the evaporator through a high pressure refrigerant line, an accumulator for collecting liquid refrigerant removed from the suction line, conduit means connecting said accumulator with the receiver and having therein a low differential pressure pump, high and low level float controls associated with said accumulator for effecting operation of said pump whenever the liquid refrigerant level in the accumulator reaches a definite high value and for stopping the pump whenever said level reaches a definite lower value, and means for effecting equalization of the pressures in said accumulator and receiver when said pump is operating.

7. In a refrigerating system provided with a compressor having a suction line for receiving refrigerant from an evaporator and also having a discharge line for delivering liquid refrigerant to a receiver communicable with the evaporator through a high pressure refrigerant line, an accumulator for collecting liquid refrigerant removed from the suction line, conduit means connecting said accumulator with the receiver and having therein a low differential pressure pump, means for effecting operation of said pump whenever the liquid level in said accumulator reaches a definite height and for stopping the pump whenever said level drops a definite amount, and means for effecting equalization of the pressures in said accumulator and receiver when said pump is operating.

8. In a refrigerating system having a compressor communicable with the suction line of an evaporator and also communicable with the high pressure refrigerant supply line of the evaporator through a receiver, an accumulatfor'for collecting liquid refrigerant from the suc.- ti'o'n' line, conduit means connecting said accumulator with the receiver andfhavin'g' therein a liquid refrigerant return by'the" pump toi'the receiver;

9,. In a refrigerating systemhaving a compressor communica'ble' with the suction line of an" evaporator and also communicable with the high pressure refrigerant supply line of the evaporator through a receiver, an accu'mula'turfor collecting; liquid refrigerant from the suctionline', conduitmeans connecting'said accumulator with the receiver and having therein a liquid refrigerant return" pump, means for establishing pressures in the accumulator' approximately equal to' the pump discharge p'ressurewhenever liquid refrigerant is being delivered by the pump to the receiver, and means for equalizing the pressures in the suction line and accumulator whenever the pump is inactive.

' T. In a refrigerating system having a compressor communicablewith the suction line of an evaporator and also communicable with the high pressures refrigerant supply pressures in the receiver and accumulator whenever the pump is delivering liquid refrigerant from the latter to the'former through said conduit means.

11- In a refris r i af y enrhaving? a compressor coin;

munlcable with this: marina and refrigerant supply Ii'e'fs" of an evaporator, artaccuml'ljiat'dt' for; collectlligdiquid refrigerant from the suction; line; conduit means onnect iug said accumulator with the refrigerantjs' pfi l"Iiiie and having therein a low difierentiaf liquid refrigerant return. pump, and means for establishing approximatelyeqfiai pressures in said conduit means onithe opposite, sides of said pump whenever'the latter is delivering-liquid refrigerant from said accumulator to the, refrigerant supply line through the conduit means. v

12. In a refrigerating system having: a compressor co municable with the suction, and ref-rigerantflsuppiv lines of an evaporator, an accumulator for collecting liquid refrigerant from' the suction line, conduit means con: necting said accumulator with the refri'g'f ant supplj' line and having therein. a low diiferen' al liquid refrigerant return pump and a non-return check valve, and means for establishing approximately equal pressures insaid conduit means, on the opposite. sides; cfsa i'd ump: wires: ever the latter is delivering liquid refrigerant; from said accumulator to the refrigerant supply line through the conduit means and past said check valve.

References Cited in the are of this patent UNITED STATES. PATENTS 

